Everyone asks: Why are windows in jet aircraft round or oval?

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This was published 6 years ago

Everyone asks: Why are windows in jet aircraft round or oval?

By Julietta Jameson




Since jet aircraft are flying at altitudes that require the cabin to be pressurised, it's vital that doors and windows create a tight seal. The difference between the pressure inside the aircraft fuselage and the pressure outside causes the fuselage to swell slightly at cruising altitude. In exactly the same way, a hydrogen-filled balloon will swell as it rises until it finally bursts. In an aircraft, this swelling results in stress to the airframe. If a window is square or rectangular, that stress is greater at the corners of the windows, and can cause it to fracture. The earliest iterations of the de Havilland DH106 Comet, the world's first passenger jetliner, did have square windows but these proved to be its downfall, literally. Two fatal crashes were attributed to airframe failure with dangerous stresses at the corners of the square windows and installation methods pinned as the cause. Round or oval windows present less of a barrier to the smooth flow of stress in a fuselage and since those crashes, windows on commercial jet aircraft have been round or oval. Improved aircraft manufacturing techniques have allowed windows to become progressively larger over time, and in particular aboard new generation aircraft such as the Airbus A350 XWB and Boeing's Dreamliner. These aircraft, which are constructed from carbon fibre composite material, have more taut airframes, and are less subject to stress, which allows larger windows to be installed.

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